Distribution of foraging by female Antarctic fur seals

Abstract

The study examined the distribution of critical habitat for foraging by female Antarctic fur seals breeding at the island of South Georgia. Bathymetric features of the continental shelf around the island of South Georgia were an important indicator for the localisation of foraging. This pattern was consistent among years of different prey availability. Lactating females were constrained to forage mainly within 100 km of the location at which the offspring was being raised. When this constraint was removed at the end of lactation, females foraged to much greater ranges and dispersed to specific regions of the continental shelf east of Patagonia (>1000 km) and to the northern edge of the Antarctic pack ice (500 km). The empirical distribution of foraging during the breeding season was used to develop a function that described the foraging distribution for the whole breeding population of females. The result was consistent with past observations from ship-based surveys and it allowed estimation of the spatial impact of breeding female fur seals on krill at South Georgia. This suggested that, in extreme cases and assuming that krill influx is limited, female fur seals could eat most of the krill present in some regions where they forage intensively. However, mean consumption was about one-tenth of the mean density of krill.

Summer foraging areas for lactating New Zealand sea lions Phocarctos hookeri

“…Lactating female Antarctic, New Zealand and Australian fur seals Arctocephalus gazella, A. forsteri and A. pusillus doriferus, respectively; and Australian and California sea lions Neophoca cinerea and Zalophus californianus, respectively, also forage over continental shelves or in relation to the edge of the shelves, close to breeding sites (Harcourt et al 1995, Gales & Costa 1997, Arnould & Hindell 2001. The geographic preference for foraging in shallower shelf waters and at shelf edges displayed by otariids usually results in foraging occurring within 100 km of breeding sites (A. gazella, Boyd et al 2002, Guinet et al 2001; South American sea lions Otaria flavescens, Campagna et al 2001, Thompson et al 1998A. forsteri, Harcourt et al 1995A.…”

“…However, this value must be interpreted with caution as it was calculated from travelling speeds that were filtered to be no greater than 2 m s -1 . The majority of otariid swim speeds fall within a range of 0.7 to 2.7 m s -1 (Arctocephalus gazella, Boyd et al 2002; Otaria flavescens, Thompson et al 1998, Campagna et al 2001Arctocephalus tropicalis, Georges et al 2000). This suggests that NZ sea lions are restricted by physiological constraints for travelling speed similar to most other otariids.…”

Change in the foraging strategy of female South American sea lions (Carnivora: Pinnipedia) after parturition

“…In this scenario, lactating otariid females are expected to modify their foraging behaviour (prey choice, time spent foraging) in order to make foraging trip duration as short as possible while they are feeding pups more or less continuously to meet their energy requirements (Costa, 2008). These trade-offs may constrain otariid females to forage closer to the rookery during early lactation, thus promoting a dietary shift after parturition that may lead them to exploit prey not consumed throughout the year (Merrick and Loughlin, 1997;Boyd et al, 2002).…”

Investigating foraging utilization distribution of female New Zealand sea lions, Auckland Islands

“…4). Colony-specific foraging areas have been documented for Antarctic fur seals (Boyd et al 2002) and specific foraging areas from breeding sites on the same islands for Northern fur seals (Robson et al 2004). Dundas and Enderby Island females do not show entirely distinct colony-specific foraging areas, as there is a large overlap in area and the number of females that forage in the north/ north-east part of the Auckland Island shelf.…”